The present invention relates to communications networks, asymmetrical communications networks, and specifically to a forward error correction (FEC) regulation system and method that offers increased performance by using variable rate (FEC) based on position location information. The FEC regulation system is applicable to public safety communications, Home Land Defense (HLD) communications, military communications, and other communications applications.
The co-filed application is for a public safety and homeland defense communications system using asymmetric receive and transmit channels. The system is an asymmetrical hybrid communications system using digital television (DTV) assets such as the Public Television (PTV) network for delivering wide bandwidth data and a land mobile radio system (LMRS) for receiving narrow bandwidth requests for the wide bandwidth data from a mobile client. The asymmetric communications system has the ability to efficiently provide data broadcasts, Amber alerts, graphics, and video transmission and retrieval to the mobile client. The mobile client may be any vehicular system or any system for a person on foot.
Currently there are very few if any practical options for realtime forward error correction (FEC) rate control in the asymmetric public safety communications network using a DTV system to broadcast to the mobile client and LMRS to receive messages from the mobile client. Continuous DTV channel measurements may be reported using the LMRS. However it is highly undesirable to use a valuable and many times congested LMRS as a continuous or periodic connection for reporting the DTV channel conditions or as a frequent ARQ (automatic retransmission request) channel. Land mobile radio bands are a scarce commodity and must remain open for vital voice communications. Thus there is a need for providing reception quality data feedback on the DTV broadcast channel without placing an undue traffic burden on the LMRS.
Additionally for reporting channel conditions the narrowband back channel LMRS contains a significant amount of network latency by design. This poses a problem for a system that uses interleave techniques under mobile conditions in urban canyons as an example. With current FEC methods, there is no provision to provide a mobile client vehicle dynamic FEC needs as it moves about. A mobile client may be headed for an area having high LOS (line-of-sight) blockage conditions. With current day methods, the signal becomes blocked or compromised first and this information is fed back to a transmitter. FEC adjustments are reactive in this case and can result in high channel inefficiency and poor performance particularly if the feedback channel is relatively slow. In this case the signal may become blocked or attenuated and new interleave and data payload redundancy is desired. However in the asymmetric communications system case, the LMRS may take tens of seconds at best to inform the DTV system to use a stronger redundancy and interleave time period for example but this is too slow and not enough benefit to justify constant LMRS use as the mobile client moves about. This is inefficient use of both the DTV and LMRS channels. FEC rates need to be regulated or controlled in a more predictive improved realtime manner for terrestrial asymmetric DTV/LMRS systems in order to make efficient use of the channel while maintaining a robust link.
There is a need to regulate or control FEC rates in a more real-time manner for terrestrial asymmetric DTV/LMRS systems and other communications systems in order to make efficient use of the channel while maintaining a robust communications link.